As is well known, trucks that have container bodies with enclosed cargo spaces often include lighting systems that illuminate the cargo spaces while personnel are loading and unloading cargo. Especially in the case of long haul trucks, truck bodies tend to be long relative to their height and width. Given height and width constraints imposed by bridge clearances and lane widths, respectively, length is the only cargo space dimension that can be increased to provide desired cargo capacity. The longstanding practice in lighting the interior of truck cargo spaces has been to mount a plurality of incandescent lamps in the cargo space roof and to space the lamps from each other from front to rear. Such lighting fixtures sometimes comprise a lamp housing recessed into the roof and enclosing an incandescent lamp and having a light distributing lens disposed on the housing between the housing and the cargo space so it is generally flush with the interior surface of the roof. This arrangement provides the required illumination without the light fixture intruding into the cargo space.
Conventional incandescent lighting systems of the type described above have been found to be unsatisfactory for use in truck cargo spaces because they waste energy, require excessive maintenance and are sometimes used in a way that creates a fire hazard. In addition, incandescent lamps generate a significant amount of heat. In refrigerated trucks, i.e. trucks that have refrigeration systems for cooling the cargo space, incandescent lamps transfer the heat that they generate into the refrigerated cargo space. The heat from the incandescent lamps therefore works against the refrigeration system, requiring more energy to maintain a given temperature. In addition, it is known that some truck drivers like to increase the illumination in the cargo space by replacing the standard low wattage incandescent lamps with higher wattage lamps. The higher wattage lamps give off more heat and do not last as long. This practice adds to bulb replacement cost. The conventional incandescent lighting system can constitute a fire hazard when used in a truck body loaded with flammable cargo--especially when such cargo is stacked up close to the incandescent lamp fixtures and the lights are inadvertently left on for a long time. Such conditions can cause truck fires that are not only dangerous to life and limb but also constitute increased costs to the trucking industry because of loss and increased insurance premiums.
There has been a longstanding need in the trucking industry for a safe, effective and energy efficient lighting system for the cargo space in a container body of a truck.
In the prior art, certain fiber optic or "light pipe" systems have been proposed for use on vehicles. For example, the Johnson et al. U.S. Pat. No. 4,947,293 granted Aug. 7, 1990 discloses a clearance lighting system for a semi trailer cargo container body. The lighting system includes a core light conducting material in the form of an elongated light conducting strip provided with a cladding material to provide a light guide. The core and cladding are constructed to provide lateral light emission as well as longitudinal propagation. A light source is adapted to end-illuminate the light guides for both sides of a container body from a single light source. A similar system that also provides a message panel is disclosed in Johnson U.S. Pat. No. 5,122,933 granted Jun. 16, 1992.
The Moore et al. U.S. Pat. No. 4,740,870 granted Apr. 26, 1988 describes a fiber optic lighting system for boats. In this system, a plurality of fiber optic cables extends from a central light source to respective plurality of remote light fixtures to provide lighting at different locations on the boat.
The Davenport et al. U.S. Pat. No. 4,811,172 granted Mar. 7, 1989 describes an optical fiber lighting system particularly suited for automobiles and aircraft. The lighting system comprises subsystems suitable for high and low beam illumination and rear illumination of an automobile. Each subsystem comprises a high intensity light source coupled to one end of each of a plurality of light pipes with each having their other end positioned relative to a reflective element and a lens. The reflective elements are arranged to provide a prescribed illumination pattern.
The Finch et al. U.S. Pat. No. 5,184,883 granted Feb. 9, 1993 discloses an automobile lighting system similar to that described in the above-referenced Davenport U.S. Pat. No. 4,811,172. The Finch et al. patent describes an indicating device that comprises a shutter having an opaque portion, a light blocking position in which the opaque portion blocks the passage of light from the output end of a light guide to a lens and a non-blocking position in which light is allowed to pass through the indicating device to the lens.
U.S. Pat. No. 5,495,400 discloses an optical fiber device that discloses the use of light pipes to illuminate exterior auto body parts such as the sides of pickup and flat-bed trucks and the rear of semi-tractor trailers. One embodiment discloses a holder configured to support a light pipe on top of the side rails of a pickup truck bed. The holder includes a flat elongated base portion that connects to the top of a side rail and a longitudinal arcuate race or channel. The race has a continuous C-shaped cross section and is configured to receive a light pipe in frictional engagement. The race is made of a rigid, optically transmissive material. The race protrudes integrally upward from along the base portion so that the race, and any light pipe engaged within the race, are supported in an upwardly-projected position exposed to repeated contact with cargo during loading, transport and unloading.
A fiber optic cargo area lighting system for trucks disclosed in U.S. Pat. No. 5,483,427, assigned to the assignee of the present invention. This patent discloses a light source mounted on the truck body and plural lighting fixtures mounted to the roof of the truck body. Each lighting fixture receives light that is piped through a separate light pipe from the source to the fixture. Two sets of lighting fixtures are disposed in linear arrays extending along a line from the front to the rear of the truck body. The light pipes for one set of lighting fixtures are all disposed within a first enclosure and the light pipes for the other set of lighting fixtures are all disposed within a second enclosure. Certain sections of the enclosures have transparent lenses and certain light pipes within the enclosures emit side light through those lenses. A lighting fixture at the rear door of the truck body has an optical switch for turning the lighting fixture on or off.
Another fiber optic cargo area lighting system for trucks is disclosed in U.S. Pat. No. 5,678,914. This patent, also assigned to the assignee of this application, also discloses a truck cargo space lighting system that includes light pipes mounted in the cargo space. As described in the previous patent, each light pipe is optically coupled to an electrically energized light source and transmits light from the light source to an output end while emitting light laterally along its length. An elongated light pipe enclosure is disposed around and supports the light pipe. The enclosure comprises a mounting flange adapted to fasten the enclosure to the floor, the side walls, the front and rear walls and/or the roof of the cargo space. The enclosure includes a light-transmitting panel disposed between the light pipe and the cargo space to transmit laterally-emitted light from the light pipe into the cargo space. The light transmitting panel comprises an elongated conduit for supporting the light pipe along its length. The light transmitting panel is formed into an elongated tubular shape defining the elongated conduit. The conduit includes an elongated longitudinally oriented slot for receiving the light pipe in force-fit snap-in engagement along its length. Each enclosure comprises at least two elongated segments disposed end-to-end, the light pipe extending through both segments. Each segment is integrally extruded from a single piece of the light transmissive material. The light pipe includes a cladding with an index of refraction that causes the cladding to emit light laterally thereof. The lighting system includes an end mirror disposed adjacent the light pipe output end, the mirror positioned to reflect light from the output end back into the light pipe. Because each enclosure comprises only a single piece of extruded plastic, this system is easy to manufacture. However, the enclosure segments of the lighting system disclosed in the '914 patent require that a light pipe be installed in the conduit portions of the segments before the segments and light pipe can be installed in a truck cargo space.
What is needed is an improved lighting system for the cargo space of a truck that is easier to install and that protects illuminating elements from damage due to cargo loading, unloading and shifting in transport.